Practical Considerations in the Use of FFT Methods for Computing Terrain Effects

Abstract

A great deal of material has been published on FFT methods in geodesy during the past few years, including a fine review by Schwarz, Sideris and Forsberg (1990). This interest is well justified by the computational efficiency of the methods, and procedures which were once theoretical curiosities can now be used on an every-day basis. Two other factors are contributing to the accuracy and importance of the methods. These are the availability of high degree spherical harmonic expansions of the earth’s gravity potential and topography, and of accurate fine-grained digital topographic data bases, such as the U.S. Geological Survey’s digital elevation models at 30 m resolution. The former allow the long wavelength components, which may not be handled well by the FFT methods, to be removed while the latter, which contain significant information down to the finest resolution, present an opportunity to improve the accuracy of gravity modeling at the expense of having to use large data bases and very efficient computational algorithms.